The invention relates to a process for separating one or several volatile component(s) from a substance mixture, in which the substance mixture is heated, the volatile component(s) is/are at least partially evaporated and the then formed vapor is condensed. In addition, the invention relates to a device suitable for performing said process.
The pre-requisites for distillation processes of the mentioned type are that the component(s) to be separated has/have a lower boiling point than the other component(s) of the substance mixture and that with respect to the component(s) to be separated, a vapor pressure gradient is maintained between the location of the evaporation and the location of the condensation.
The term “flash distillation” generally means a vacuum distillation technique in which evaporator and condenser are arranged in one and the same vessel in such manner that the vapor molecules travel a short path from the location of the evaporation to the location of the condensation. Normally, the distance between evaporator and condenser surface in industrial flash distillation apparatuses amounts from a few centimeters up to several decimeters. If the distance between evaporator surface and condenser surface is smaller than the average free path length of the vapor molecules, one talks of molecular distillation.
Based on low operating pressures, flash distillation and molecular distillation are, among others, excellent methods for distillative separation of one or several volatile components from bi- or multi-substance mixtures with low operating temperatures. The method, however, always reaches its limitation if the vapor pressure of the distilled component or components on the condensation surface reaches the partial pressure of the corresponding component(s) in the mixture on the heated evaporator wall. Further separation of the volatile component(s) is then no longer possible, since, according to the understanding of flash distillation, the driving force, i.e. the pressure difference, is lacking, or according to the understanding of molecular distillation, the evaporation rate at the evaporator surface corresponds to the evaporation rate of the respective component(s) on the interior condenser. Further lowering of the interior condenser temperature in order to reduce the vapor pressure of the volatile component(s) over the condensate flow on the interior condenser is frequently not possible, because the condensate would solidify, for example.